Synopsis

Simultaneous-Multi-Slice
Turbo-Spin-Echo (SMS TSE) protocols were added to our conventional (CNV) hip
joint MR examination in 21 patients. Image quality of acetabular labrum,
articular cartilage, round ligament and bony trabeculae were evaluated by three
reviewers and showed comparable image quality, whereas SMS was slightly better
for bony trabeculae. If CNV is substituted by SMS, total scan time can be
reduced by approximately 40%. Although SMS protocols showed higher specific
absorption rate (SAR), it only accounted for 20% of scans which exceeded the first
level of SAR limit. SMS could be applied to clinical examination with advantage
of acquisition time reduction.

PURPOSE

MR
imaging to delineate the fine components of the hip joint requires superb
imaging quality with high spatial resolution. However, this tends to prolong
the acquisition time. The SMS technique using multiband excitation pulse enables
substantial reduction of the time
required according to the number of slices. When SMS is utilized for scan time
reduction with the TSE sequence, which is most widely used for joint imaging,
scan parameters related to image contrast (e.g.TR) are changed. Moreover, SAR
is increased. The purpose of this study was to prospectively compare the hip
joint TSE imaging with and without SMS regarding acquisition time, imaging quality
and SAR.

METHODS

This study was approved by the local ethics committee,
and written informed consent was obtained from all patients prior to the MR examinations.
MR examination was performed on a 3-T whole-body scanner (MAGNETOM Skyra ;
Siemens Healthcare GmbH, Erlangen, Germany), and an 18-channel Body coil.
Twenty-one patients (4 males, 17 females, average age of
51.5 years, age range: 22 to 76 years), who had hip pain and were suspected to
have acetabular labral damage, underwent unilateral hip joint MR examination.
In addition to our routine protocols of oblique
coronal proton-density-weighted (PDW) 2D TSE, axial T1-weighted (T1W) TSE and
oblique coronal fat-saturated T2-weighted (FS-T2W) TSE, prototype SMS TSE
protocols using a prototype SMS TSE were also acquired in the identical
geometry (Fig.1 and 2). At the time, system predicted SAR values of each
protocol were recorded before the actual scan. therefore there was no actual
scan between SAR prediction with and without SMS protocol and they were done in
as short a time as possible. A two-sided paired Student’s t-test was used for
statistical evaluation. Three board-certificated radiologists evaluated the set
of the images with and without SMS for imaging quality of these components:
acetabular labrum, articular cartilage, bony trabecula within the femoral neck
(only for PDW and T1W), and the round ligament (only for FS-T2W), independently
and blindly. The quality was rated using five-point scales; CNV+2 = CNV is superior
to SMS, CNV+1 = CNV is slightly superior to SMS, EVEN = CNV is equal to SMS,
SMS+1 = SMS is slightly superior to CNV, SMS+2 = SMS is superior to CNV. Inter-observer
agreement for the qualitative rating was calculated using Spearman's rank correlation
coefficient test. Data analysis was performed with JMP® 12 (SAS Institute Inc.,
Cary, NC, USA). A p-value of less than 0.05 was considered significant.

RESULTS

SMS imaging reduced the acquisition time of the total
three sequences from 12m16s to 7m35s. Total combined cases of the imaging quality
are in Fig. 3. Total 41 cases (68.3%) out of 60 cases were rated as EVEN for
delineating the acetabular labrum with PDW, whereas 13 cases (21.7 %) were
rated as CNV+1 , 6 cases (10%) as SMS+1, no case was rated as CNV+2 or SMS+2.
SMS for delineation of bony trabecular was evaluated slightly better than CNV.
No significant correlation in three radiologists scores was found, except for
the acetabular labrum with PDW, (rs=0.6023 and p-value = 0.0049). SMS indicated
high SAR values of approximately 80-90 % of the simulated limit (Fig. 4). They
were significantly higher than CNV (p<0.001 for all sequences).

DISCUSSION

SMS indicated relatively equal imaging quality to CNV
imaging for delineation of acetabular labrum, articular cartilage, and the
round ligament, whereas, slightly better for bony trabecular demonstration. By
using SMS, approximately 40% reduction of the acquisition time may provide advantage
for clinical MR examinations of the hip joint. Shorter examination time can
contribute to increase the examination throughput or be exploited to improve
the spatial resolution or SNR.

CONCLUSION

With significant reduction of the acquisition time,
and with comparable image quality to CNV imaging, SMS can be applied to the
clinical MR examination of the hip joint.

3.Crema MD, et al. A narrative overview of the current status of MRI of the hip and its relevance for osteoarthritis research - what we know, what has changed and where are we going? Osteoarthritis and Cartilage (2016),2016 Sep 13. pii: S1063-4584(16)30275-8.